ID   4.6.1.25
DE   bacteriophage T4 restriction endoribonuclease RegB.
CA   a [pre-mRNA]-containing guanosine-adenosine + H2O = a 5' hydroxy-
CA   guanosine-[pre-mRNA fragment] + a [pre-mRNA fragment]-3'-adenosine-
CA   3'-phosphate.
CC   -!- The enzyme from bacteriophage T4 cleaves early mRNAs between Ap and
CC       Gp at one specific specific GpGpApGp site, favoring their further
CC       transition to middle-phase mRNA.
CC   -!- The activity is enhanced by Ribosomal S1 protein.
CC   -!- The enzyme catalyzes a two-stage endonucleolytic cleavage.
CC   -!- The first reaction produces 5'-hydroxy-phosphooligonucletides and
CC       3'-phosphooligonucleotides ending with 2',3'-cyclic phosphodiester,
CC       which are released from the enzyme.
CC   -!- The enzyme then hydrolyzes these cyclic compounds in a second
CC       reaction that takes place only when all the susceptible
CC       3',5'-phosphodiester bonds have been cyclised.
CC   -!- The second reaction is a reversal of the first reaction using the
CC       hydroxyl group of water instead of the 5'-hydroxyl group of ribose.
CC   -!- The overall process is that of a phosphorus-oxygen lyase followed by
CC       hydrolysis to form the 3'-nucleotides.
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